The efficiency of many surgical procedures could be improved if there was a safe way to automatically stop the action of the surgical tool when it encounters an organ or type of tissue that should not be disturbed. For example, during liposuction a cannula, inserted via a minimal incision, is moved rapidly across fatty tissue in order to remove fat by using suction. Aggressive use of the cannula may result is a perforated organ and even death. On the other hand, slow movements significantly extend the duration of the surgery. A similar situation exists when using en electro-surgical tool or even an ordinary scalpel to cut in the vicinity of an organ that should not be damaged. The action of an electro-surgical tool can be stopped instantly (by stopping the current flow) if the tool could detect that it is touching or approaching a type of tissue that should not be cut. It has been known that different body tissues have different electrical properties, and the type of tissue, and even the state of the tissue can be determined from such electrical measurements. By the way of example, studies demonstrated that cancerous tissue has different electrical properties from healthy tissue. The field of tissue discrimination by electrical methods is known as “Bioimpedance Spectroscopy” and a good survey article is: “The Dielectric Properties of Biological Tissues: Literature survey” by Gabriel and Corthhout (Phys. Med. Biol. 41, 1996, pp. 2231-2249). This article is hereby incorporated by reference. Also incorporated by reference is US patent application 2007/0270688 which shares common inventors with this application. It is known that much of the information is in the way the impedance, and in particular the dielectric constant (also known as permittivity) changes with frequency. By measuring the electrical properties at multiple frequencies, typically in the range of KHz to MHz, a “signature” is derived which uniquely identifies the tissue.
In some procedures the ability to apply energy such as heat, ultrasound, microwaves, water jets and others energy sources is limited by the fear of directing the energy to the wrong organ or tissue. For example, it is known that heating up the fat during liposuction will liquefy it and make it easier to remove, but if a heated cannula is used it can cause burns to other tissues. It is desired to have a method of supplying the energy to the surgical tool as long as it is in contact with the correct tissue, instantly stopping the energy when the wrong type of tissue is touched.
Because of the relative slowness of human response time, it is desired to have the corrective action taking place automatically rather than simply alarming the surgeon. For example, when moving a cannula it is desired to instantly stop the motion of the cannula when the wrong tissue is touched, rather than sounding an alarm and relying on the response time of the surgeon.